Effects of impact loadings on a submerged floating tunnel: Experimental and numerical investigations

Dynamic responses of a scaled segmental submerged floating tunnel (SFT) subjected to pendulum-type impact loadings are investigated through a combination of experimental tests and numerical simulations. In the experimental program, displacement responses of the moored SFT model were first examined under impacts applied at the upper, central, and lower parts of the tunnel. Additional tests were conducted by releasing the tension in the mooring lines. The scaled tunnel was fixed at the top and subjected to twelve cases combining three different impactor masses with four initial pendulum angles, enabling direct measurement of impact forces. Structural displacements, mooring line tensions, and impact forces were systematically analyzed to evaluate the dynamic behavior of the SFT under various loading conditions. For the numerical modeling of pendulum impact tests, appropriate buoyancy representation and fluid mesh discretization were identified as critical parameters. Different modeling strategies were assessed, and the most effective combination was selected to obtain accurate results. To ensure accurate contact modeling under diverse impact conditions, the penalty scale factor was calibrated by comparing predicted impact forces with experimental measurements. A cubic polynomial relationship between the penalty scale factor and initial impact velocity was established and extended to the full-scale prototype to provide a practical guideline for contact parameter selection. The calibrated numerical model reproduced the observed responses with prediction errors consistently below 7%. A reliable approach for assessing SFT impact behavior is established by the experimental methodology and verified simulation framework presented in this study. These methodologies not only enhance the efficiency of SFT design and safety evaluation but also provide a foundation for impact studies of other submerged buoyant structures.